Bone cements, particularly such used to anchor artificial joints, contain x-ray contrast mediums for clinical progress control purposes. Such x-ray contrast mediums allow the surgeon to safely monitor the implant and offer an early diagnosis for possible complications, such as e.g. loosening. Bone cements are chemical resins on acrylate basis (for example Palacos® R from Heraeus Kulzer GmbH & Co. KG). They are offered as two-component systems with a powdery polymer mixture and a liquid monomer. As the contrast agents, zirconium dioxide or barium sulfate are added to the polymer mixture. These x-ray contrast mediums however are not incorporated in the polymer chain and therefore are considered the possible cause for micro-cracks in the cement casing. Zirconium dioxide may possibly have an abrasive effect on contact surfaces.
EP 41 614 describes coated BaSO4 powder for dental fillings, which is prepared by dispersing and adding a polymer solution. EP 89782 describes coated barium sulfate, which is produced by mixing PPMA particles and BaSO4 particles with HEMA and subsequent heating. JP 06024927 relates to polymer filler composites, which are prepared by the polymerization of an acid monomer and another unsaturated monomer in the presence of x-ray contrast medium powder.
WO 0057932: This document describes composites made of a polymeric matrix and solid, liquid or gaseous fillers, which exhibit a “matrix ligament thickness” of preferably less than 250 nm. This signifies the distance between the filler particles. The nano-composites can be produced by introducing the filler into the precursors of the cement, introducing them during the mixing process of the precursors, or introducing them into a prefabricated paste, dough or liquid, where polymerization is induced. The fillers can be radio-opaque, e.g. zirconium oxide.
The examples prove composites with the following particles: 1–3 micrometer BaSO4, 100 nm BaSO4, and 60 nm Al2O3 (acrylic-coated).
EP 644 780: Claim 12 relates to a granulate or fibrous material, where the filler particles (size of 1–15μ) are enclosed at least partially by the (co)polymeric matrix, wherein the polymer chains are not cracked. The material can be produced through mixing and extrusion.
U.S. Pat. No. 6,080,801 reveals polymer granules (FIG. 1) with micro-fillers embedded partially or completely therein. These granules are no larger than 300μ and contain filler particles of the size 1–250, preferably 5–15μ. They are produced e.g. when the filler particles form crystallization nuclei during polymerization.